1. Field of the Invention
The present invention relates to a sapphire substrate, in particular to a sapphire substrate with patterned structure, which can be used in ultraviolet light-emitting diode (UV-LED).
2. Description of the Related Art
In recent years, the ultraviolet light emitting diode (UV-LED) has been attracted considerable attention due to their wide range of applications such as air or water purification, disinfection, medical phototherapy. High quality aluminum nitride (AlN) layer is commonly used as a crucial template layer between a sapphire substrate and aluminum gallium nitride (AlGaN) layer for the growth of AlGaN-based UV-LED. However, the AlN layer on a flat sapphire substrate usually suffers from very high threading dislocation densities (TDDs) due to the large lattice mismatch and thermal expansion mismatch between AlN and sapphire. To achieve high efficiency UV-LED, the development of a low-TDD AlN layer is very important because the TDDs in multi-quantum wells act as non-radiative recombination centers.
Various methods have been developed to reduce the TDDs, and one of the methods to reduce the TDDs is lateral epitaxial overgrowth (LEO) technique. LEO-AlN layer is usually grown on the patterned sapphire substrate (PSS), which can reduce the number of TDDs in the LEO-AlN layers. However, the LEO-AlN layer on the PSS requires a large coalescence thickness for the LEO-AlN layer and greatly increases the epitaxial time and cost. Besides, serious roughness is usually observed in the LEO-AlN layer grown on the PSS, which may affect subsequent growth of AlGaN-based UV-LED.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person having ordinary skill in the art.